Rice hull burners

ABSTRACT

Apparatus for continuous burning of light combustible materials such as rice hulls under closely controlled condition, including a combustion chamber, means for feeding the combustible material and air to the chamber base and an agitator for dispersing the combustible material so that it is ignited and simultaneously carried upwardly through the combustion chamber. Use of the burning apparatus is further contemplated in combination with means for curing ash produced in the combustion chamber.

.United States Patent 2,653,554 9/l953 Hatton et al. l l0/29 FOREIGN PATENTS 485,763 5/l938 Great Britain 1 10/29 858,107 1/1961 Great Britain l 10/28 Primary ExaminerEdward G. Favors Anomey- Fryer, Tjensvold, Feix, Phillips & Lempio ABSTRACT: Apparatus for continuous burning of light combustible materials such as rice hulls under closely controlled condition, including a combustion chamber, means for feeding the combustible material and air to the chamber base and an agitator for dispersing the combustible material so that it is ignited and simultaneously carried upwardly through the combustion chamber. Use of the burning apparatus is further con- Reierences Cited UNITED STATES PATENTS templated in combufiaticgn with means for curing ash produced in the combustion c am er. 2,452,844 1 1/1948 Es naulEP elteri e 1 10/29 V m I g i I 33 r g r I I I I z a l j i f 36 "I8 as 37 2s B \2, w 24 I I 23 I I w 2 a 2 Sheets-Sheet 1 INVENTOR. C ORIAN R. GARDNER BY ?/z,7x/v, W 25/50,

ATTORNEYS RICE HULL BURNERS The present invention relates to apparatus for burning relatively light combustible materials. The invention permits close variable control over combustion characteristics such as temperature and duration. Such control is desirable to permit complete combustion and also to regulate physical characteristics of ash produced from the combustible materials.

The present invention is particularly contemplated for combustion of light grain products and more particularly for the burning of rice hulls to produce ash having suitable physical properties for various applications. It will be apparent from the following description that the apparatus may also be employed for burning other light materials generally similar to rice hulls.

During harvesting of rice, the rice kernels are removed from their hulls to produce a suitable food product.- The hulls, which are particularly troublesome and difficult to handle because of their low density and tendency to cling to each other, are commonly disposed of by burning. Numerous uses have arisen for the combustion products of the rice hulls. Rice hull ashes are used as a constituent in soaps and as an absorbent material or sweeping compound employed .for example to clean oil and grease from floors and other surfaces in garages and automobile service areas.

The physical properties of the ash are particularly important for absorption application. The absorption characteristics of the ash have been found to be dependent on physical properties of the ash such as its density and particle size, for example. These properties may be controlled and varied by the apparatus and process of the present invention to provide optimum absorbency in the ash.

in the prior art, the hulls have generally been burned by piling them in contained stacks and igniting them. Usually, concrete or steel buildings are filled with the hulls which are then ignited. Combustion is generally uncontrolled and continues for days or even weeks before the hulls are converted to a suitable ash. This method has been found undesirable because of the time involved, the necessity of maintaining buildings for the burning and the resulting lack of economy. Further, it is difficult if not impossible to accurately control the combustion and maintain physical properties of the ash within selected limits.

Also, because of the lack of control over the burning hulls, large quantities of smoke tend to be emitted. This is a particular problem in view of the increasingly important antipollution laws prohibiting the release of smoke andother debris into the atmosphere.

The apparatus of the present invention permits materials such as rice hulls to be burned in a generally unattended operation while controlling process parameters such as temperature and duration of combustion so that properties of the solid combustion product or ash may be maintained within desired limits.

As contemplated by the present invention, the material to be burned is fed at a controlled rate from storage means into a generally vertical combustion chamber at least partially under gravity flow conditions. The material is generally dispersed throughout the base of the combustion chamber by an agitator. Air to support the combustion is also introduced at the base of the combustion chamber so that it tends to maintain dispersion of the material and direct it upwardly through the combustion chamber while it is burning.

The present invention as summarized above offers numerous operating advantages. The combustion parameters may be varied, for example, by altering the rate at which the material enters the combustion chamber, the rate at which air enters the chamber, the effective vertical length of the chamber and the degree of agitation at the base of the combustion chamber. Close control over the combustion products is thereby afforded. Clean burning of the hulls is therefor permitted by the present invention which eliminates or minimizes the release of pollutants into the atmosphere.

The operation may continue generally unattended after the combustion parameters are established and as long as a supply of material to be burned is maintained.

The invention also permits operating economy in other ways. For example, convection currents in the combustion chamber tend to induce an increased rate of air flow into the base of the combustion chamber. Thus, a relatively small blower may be employed for directing air to the combustion chamber.

Accordingly, it is an object of the present invention to provide apparatus for the control burning of relatively light combustible materials such as rice hulls.

It is a further object to provide such a burner wherein the operating parameters may be easily varied and controlled.

It is a still further object to provide such a burner wherein the combustion process may continue generally unattended for extended periods of time.

It is an additional object to carry out the combustion in a generally vertical chamber wherein material to be burned is introduced and dispersed at the base of the chamber along with air for supporting the combustion.

It is also an object to provide apparatus for feeding the material into the combustion chamber at a controlled rate and at least partly under the effects of gravity to avoid undesirable packing of the material.

It has further been found that properties of the ash may be substantially varied by suitably curing the ash after burning. Accordingly, still another object is the provision of apparatus for curing the ash in combination with the combustion apparatus set forth above.

The above objects and advantages are believed to be clarified and additional objects and advantages made apparent by the following description having reference to the accompanying drawings.

IN THE DRAWINGS FIG. 1 is a view in elevation of the present burning apparatus with portions broken away to more clearly show its internal construction; and

FIG. 2 is a view of a burner similar to that of F 1G. 1 with associated curing apparatus.

A preferred embodiment of the present invention as shown in FIG. 1, is particularly suited for the burning of rice hulls. it will be apparent, however, that the present invention may be readily adapted for the burning of other light materials such as by-products of various grains, for example. For the burning of other such materials, it may be desirable to vary operating parameters according to the present invention and the principles of operation set forth below.

Referring now to FIG. 1, a housing 11 defines a combustion chamber 12 with combustible material from a hopper 13 delivered to the base of the combustion chamber 12 by a feed duct 14. Air under pressure is also delivered to the base of the combustion chamber from a blower 16 through a plurality of ports 17. Rice hulls exiting the feed duct 14 are dispersed by an agitator 18 driven by a motor 19. The dispersed rice hulls tend to be carried upwardly through the combustion chamber 12 by air from the ports 17. Combustion of the rice hulls takes place during their upward travel through the combustion chamber 12. Heat from combustion of the rice hull tends to assist in carrying the burned rice hulls upwardly through the combustion chamber and to draw additional air into the base of the combustion chamber through the feed duct 14.

The housing 11 forming the combustion chamber 12 is preferably formed as a vertical cylinder of structural steel, for example, supported by framework indicated at 21. The motor 19 is mounted by brackets 22 on the framework 21. The motor 19 is attached in driving relation to the agitator 18 by means of reduction gearing 23, a coupling 24 and a drive shaft 25 which is also rotatably supported by a bracket 26 mounted upon the framework 21.

The feed duct 14 is formed by a cylindrical steel pipe 27 extending vertically downwardly from the hopper 13 towards the base of the combustion chamber 12. The base of the tube 27 is open so that combustible material may pass from the feed duct 14 toward the agitator 18 at the base of the combustion chamber. The present invention particularly contemplates that large quantities of rice hulls or other combustible material be available to the hopper 13 to feed the burner over long periods of operation. Accordingly, to control the rate of feed for combustible material entering the combustion chamber 12, an adjustable gate 28 is arranged within the top of the tube 27 to control the flow of material from the hopper 13.

The blower 16 may be of any conventional motor driven type. The blower 16 is connected to an inlet pipe 31 which in turn is connected to an air duct 32 concentrically formed around the feed duct cylinder 27 by another cylindrical member 33. The air outlet ports 17 are formed at the base of the cylinder 33 so that air is delivered to the base of the combustion chamber 12. Deflector rings indicated at 34 may be employed adjacent the outlet ports 17 to assure its upward passage through the combustion chamber, particularly at the time of ignition. The agitator 18 of FIG. 1 is comprised of two blades 36 mounted upon the shaft 24 by a transverse bar 37. The blades 36 are angled at approximately 30 to better disperse the rice hulls and direct them upwardly into the combustion chamber for entrainment with air exiting the outlet ports 17.

The top of the cylinder 11 is open around the air duct cylinder 33. The concentric cylinders 27, 33 and the hopper 13 are supported within the combustion chamber by external framework which is not shown in order to simplify the drawing. The rice hulls pass upwardly through the combustion chamber 12 and outwardly from the top of the cylinder 11 after burning where they may be collected by suitable means, an exemplary embodiment of which is described in greater detail with reference to FIG. 2.

To commence operation of the burner illustrated in FIG. 1, the motor 19 is started to set the agitator 18 in motion and the blower 16 is started to deliver air into the combustion chamber through the outlet ports 17. Rice hulls are introduced from the hopper 13 into the base of the combustion chamber through the feed duct 14. Combustion of the rice hulls is commenced, for example, by igniting a suitable fuel such as kerosene in the base of the combustion chamber. The rice hulls dispersed by the agitator 18 and carried upwardly by air from the outlet ports 17 are rapidly ignited with subsequent combustion in the chamber 12 being supported by the introduction of additional rice hulls and air. As noted above, high temperatures of combustion developed in the chamber 12 also serve to create upwardly directed convection currents which carry the burned rice hulls upwardly and outwardly of the combustion chamber. Thus, rising convection currents within the chamber 12 serve to draw additional air into the combustion chamber from the feed duct 14 along with the rice hulls. Since this additional supply of air is drawn into the combustion chamber through the feed duct 14 by combustion of the rice hulls, only a relatively minimum amount of air need be supplied by the blower 16.

A prototype model of the present burner illustrated in FIG. 1 was constructed with the combustion chamber being approximately 24 inches long and 18 inches in diameter and the blower 16 being capable of delivering 100 cubic feet of air per minute to the base of the combustion chamber. The prototype model constructed with these dimensions had an overall height of approximately 6 feet but was found capable of producing rice hull ash at an approximate rate of at least cubic feet per hour. In addition to its compact dimensions, the present burner was found to provide for very clean and efficient burning of the rice hulls with no noticeable amount of smoke or other pollutants being introduced into the air. It is apparent that the size of the unit may be altered to alter its capacity.

It was further found that the combustion characteristics for the burner could be controlled by varying the amount of air delivered by the blower 16, the rate of feed through the duct 14, and the rotational speed of the agitator'18. The motor 19 may be of a multispeed variety in order to vary the speed of rotation for the agitator 18. One criterion for controlling combustion of the rice hulls is the temperature maintained within the combustion chamber 12. The temperature along the length of the combustion chamber 12 may be determined, for example, by various types of conventional thermal sensors (not shown). The various operating parameters for the burner may be adjusted either manually or automatically depending upon the temperatures present within the combustion chamber 12 to provide for proper burning of the rice hulls.

The burner of FIG. 1 is also illustrated at 101 in FIG. 2 in combination with means for receiving the burned rice hulls from the top of the combustion chamber 12 and curing them under suitable conditions described further below. Various components of the burner are indicated by primed numerals similar to those in FIG. 1.

The curing conditions and particularly the duration of cure are of importance for determining the finished properties of the rice hull ash. An average cure time within apparatus of the type described below may be approximately 15 hours. However, ash employed for example as a soap constituent is cured longer than ash employed in other applications such as absorbent material, for example.

It has also been found that, at least in combination with the burner described above, the ash must be cooled gradually during curing to maintain desired characteristics of the ash. This is provided for in the curing means of the present invention by collecting the ash in slowly moving containers which are preheated by the bumer 101. The containers are maintained within an enclosed curing chamber for the duration of the cure to avoid moving air currents. The cured ash is then transferred from the containers into suitable storage means.

As illustrated in FIG. 2 the burner 101 is centrally mounted on supporting structure 102 at the top of a cylindrical structure 103 fonning a generally enclosed curing chamber 104. The burner 101 is generally similar to that illustrated in FIG. 1. However, one variation from the construction of FIG. 1 is illustrated by a variable rate conveyor 106 employed to deliver the hulls to the burner at a controlled rate. In this manner, large quantities of hulls may be stored in a location remote from the burner and delivered to the burner as described to maintain proper combustion.

A dome shaped structure 107 of mesh or screen is arranged above the burner 101 to restrain ashes exiting the burner while permitting air and combustion gases to escape. The structure 107 is shaped to permit the ashes to settle and be collected in buckets 108 mounted on endless chains 109 of a plurality of conveyors, two such conveyors being indicated in FIG. 2 at l 1 land 1 12 respectively.

The endless chains supporting the buckets are trained over upper sprockets 113 arranged adjacent the top of the cylinder 11' forming the combustion chamber. Collection bins 114 and 116 are arranged at the base of the curing chamber 104 to receive the ashes from the buckets 108. The bins, for example, may be boxlike structures having spring-loaded doors 115 which are normally closed and which open as necessary to admit the buckets for dumping. The ashes may be removed as desired from the bins for example through spring loaded traps doors 120.

As noted above, the rate at which temperature of the ash is reduced during curing is important for controlling various properties of the ash. in the present apparatus, the curing step principally takes place while the ashes are in the buckets. The speed of the conveyors is adjusted so that the ashes remain in the buckets for a selected duration.

Simultaneous production of ash for different applications is permitted by operating the conveyors 1 11 and 112 at different speeds. For example, one or more conveyors may be operated at a slower speed with a longer curing duration suitable for ash employed as a soap constituent, for example. Another conveyor or conveyors may be operated at a higher speed with a shorter curing duration suitable to condition the ash for use as absorbent material, for example.

The temperature of the ash during curing is further controlled by the association of the conveyor buckets with the burner. As the buckets slowly pass over the sprockets 1 l3 and approach the burner 101, they are preheated to approximately the same temperature as the ash. The ash then collects in the preheated buckets. Preferably, the ash is permitted to collect to a substantial depth of approximately 6 to 12 inches, for example, or more to assist in controlling the rate at which the ash cools. The buckets are preferably constructed with a lining of asbestos or suitable refractory material capable of withstanding the high temperatures adjacent the burner. The lining also tends to prevent heat from being transferred too rapidly to ash collected in the bucket.

The conveyors 111 and 112 are further arranged so that the buckets 108 pass in close proximity to the burner shell 11' after they are loaded with ash. This further controls the rate at which heat initially escapes from the ash.

The curing step is then generally complete as the ash is delivered to the storage bins 116 and 117. However, additional curing may be allowed to occur within the storage bins.

The invention as disclosed above is believed to provide a substantial novel advance in the art of burning apparatus for light combustible materials such as rice hulls. A preferred embodiment of the invention is described above. However, it is apparent that numerous modifications and variations are possible within the scope of the present invention which is defined by the following claims.

What is claimed is:

1. Apparatus for burning light combustible materials under control conditions, comprising a vertically arranged, cylindrical combustion chamber being open at its top, the chamber also having a substantially continuous floor and substantially continuous sidewalls,

a feed duct extending downwardly through said chamber toward its base,

means for delivering the combustible material into the top of said feed duct,

blower means for delivering air to the base of said combustion chamber, and

agitator means at the base of said combustion chamber for receiving the combustible material and distributing it about the base of said combustion chamber and upwardly therethrough for inter-mixing with the air to permit combustion of the material as it moves upwardly through said combustion chamber, the top opening permitting substantially free passage of solid combustion products upwardly and out of said combustion chamber.

2. The invention of claim 1 wherein the means for delivering combustible material into said feed duct includes means for variably regulating the amount of material delivered thereinto.

3. The invention of claim 2 wherein said regulating means comprises adjustable gate means.

4. The invention of claim 2 wherein said regulating means comprises a variable rate conveyor.

5. The invention of claim 2 further comprising hopper means for containing the combustible material, said hopper means being communicated with said feed duct by said regulating means.

6. The invention of claim 1 wherein said feed duct is a cylindrical member having a downwardly extending, open end adjacent the base of said combustion chamber and said blower means includes an air duct concentrically formed about said feed duct, a plurality of air outlet ports being formed in the air duct at the base of said combustion chamber for passage of air from said air duct into said combustion chamber.

7. The invention of claim 6 further comprising deflector means adjacent the air outlet ports for directing air from said air duct upwardly through said combustion chamber.

8. Apparatus for burning light combustible materials such as rice hulls under controlled conditions, comprising a hollow combustion chamber being substantially open at its top,

means for introducing combustible material into the base of said chamber,

an agitator at the base of said chamber, said agitator including blade elements and being operable at sufficient speeds for receiving the combustible material and dispersing it upwardly from the base of said chamber, and

means for delivering air into the base of said chamber above said agitator and permitting the air to entrain the combustible material and support combustion thereof during its upward passage through said chamber.

9. The invention of claim ti wherein said means for introducing combustible material into the chamber comprises a conduit vertically arranged within said chamber to permit passage of the combustible material therethrough at least partially under the influence of gravity.

10. The invention of claim 9 wherein the means for introducing air comprises a plurality of ports formed about the base of said chamber for distributing the air evenly therein.

11. The invention of claim 9 wherein the means for in troducing air comprises a conduit concentrically arranged about the conduit for introducing combustible material, the annular region between the conduits being closed at the bottom thereof, a plurality of spaced apart air outlet ports being formed by the air conduit above said agitator.

12. Apparatus for burning light combustible materials such as rice hulls under controlled conditions, comprising a hollow combustion chamber having an opening at its top,

means for introducing combustible material into the base of said chamber,

an agitator at the base of said chamber for receiving the combustible material and dispersing it upwardly from the base of said chamber,

means for delivering air into the base of said chamber and permitting the air to entrain the combustible material and support combustion thereof during its upward passage through said chamber, and

means for receiving combustion products from said chamber and curing them under controlled conditions.

13. The invention of claim 12 wherein the curing means comprises a plurality of means for separately receiving the combustion products and curing them under selected conditions.

14. The invention of claim 12 wherein the curing means are arranged for at least partial preheating by heat from the combustion chamber.

15. Apparatus for burning light combustible materials under controlled conditions, comprising a vertically arranged, hollow combustion chamber having an opening at its top,

a cylinder feed duct vertically arranged in said combustion chamber and having an opening adjacent the base of said chamber for delivering combustible material to the base of said chamber,

means for delivering combustible material at a controlled rate into said feed duct,

blower means communicated with the base of said chamber by a plurality of outlet ports for evenly distributing air throughout the base of said chamber,

an agitator at the base of said combustion chamber for receiving the combustible material and dispersing it about the base of said chamber for entrainment with the air to pennit combustion of the material as it moves upwardly through said combustion chamber, and

means for receiving combustion products from said chamber and curing them under controlled conditions.

16. The invention of claim 15 wherein said curing means comprises a hollow curing chamber, a plurality of conveyors vertically arranged therein and receiving means at the base of the conveyors, said combustion chamber being arranged generally at the top of the curing chamber and further com prising means for directing combustion products from said chamber onto said conveyors.

17. The invention of claim 16 wherein the plurality of conveyors are operable at different speeds for establishing different curing conditions.

18. The invention of claim 16 wherein the tops of the conveyors are closely adjacent the combustion chamber to permit preheating thereof. 

1. Apparatus for burning light combustible materials under control conditions, comprising a vertically arranged, cylindrical combustion chamber being open at its top, the chamber also having a substantially continuous floor and substantially continuous sidewalls, a feed duct extending downwardly through said chamber toward its base, means for delivering the combustible material into the top of said feed duct, blower means for delivering air to the base of said combustion chamber, and agitator means at the base of said combustion chamber for receiving the combustible material and distributing it about the base of said combustion chamber and upwardly therethrough for intermixing with the air to permit combustion of the material as it moves upwardly through said combustIon chamber, the top opening permitting substantially free passage of solid combustion products upwardly and out of said combustion chamber.
 2. The invention of claim 1 wherein the means for delivering combustible material into said feed duct includes means for variably regulating the amount of material delivered thereinto.
 3. The invention of claim 2 wherein said regulating means comprises adjustable gate means.
 4. The invention of claim 2 wherein said regulating means comprises a variable rate conveyor.
 5. The invention of claim 2 further comprising hopper means for containing the combustible material, said hopper means being communicated with said feed duct by said regulating means.
 6. The invention of claim 1 wherein said feed duct is a cylindrical member having a downwardly extending, open end adjacent the base of said combustion chamber and said blower means includes an air duct concentrically formed about said feed duct, a plurality of air outlet ports being formed in the air duct at the base of said combustion chamber for passage of air from said air duct into said combustion chamber.
 7. The invention of claim 6 further comprising deflector means adjacent the air outlet ports for directing air from said air duct upwardly through said combustion chamber.
 8. Apparatus for burning light combustible materials such as rice hulls under controlled conditions, comprising a hollow combustion chamber being substantially open at its top, means for introducing combustible material into the base of said chamber, an agitator at the base of said chamber, said agitator including blade elements and being operable at sufficient speeds for receiving the combustible material and dispersing it upwardly from the base of said chamber, and means for delivering air into the base of said chamber above said agitator and permitting the air to entrain the combustible material and support combustion thereof during its upward passage through said chamber.
 9. The invention of claim 8 wherein said means for introducing combustible material into the chamber comprises a conduit vertically arranged within said chamber to permit passage of the combustible material therethrough at least partially under the influence of gravity.
 10. The invention of claim 9 wherein the means for introducing air comprises a plurality of ports formed about the base of said chamber for distributing the air evenly therein.
 11. The invention of claim 9 wherein the means for introducing air comprises a conduit concentrically arranged about the conduit for introducing combustible material, the annular region between the conduits being closed at the bottom thereof, a plurality of spaced apart air outlet ports being formed by the air conduit above said agitator.
 12. Apparatus for burning light combustible materials such as rice hulls under controlled conditions, comprising a hollow combustion chamber having an opening at its top, means for introducing combustible material into the base of said chamber, an agitator at the base of said chamber for receiving the combustible material and dispersing it upwardly from the base of said chamber, means for delivering air into the base of said chamber and permitting the air to entrain the combustible material and support combustion thereof during its upward passage through said chamber, and means for receiving combustion products from said chamber and curing them under controlled conditions.
 13. The invention of claim 12 wherein the curing means comprises a plurality of means for separately receiving the combustion products and curing them under selected conditions.
 14. The invention of claim 12 wherein the curing means are arranged for at least partial preheating by heat from the combustion chamber.
 15. Apparatus for burning light combustible materials under controlled conditions, comprising a vertically arranged, hollow combustion chamber having an opening at its top, a cylinder feed duct vertiCally arranged in said combustion chamber and having an opening adjacent the base of said chamber for delivering combustible material to the base of said chamber, means for delivering combustible material at a controlled rate into said feed duct, blower means communicated with the base of said chamber by a plurality of outlet ports for evenly distributing air throughout the base of said chamber, an agitator at the base of said combustion chamber for receiving the combustible material and dispersing it about the base of said chamber for entrainment with the air to permit combustion of the material as it moves upwardly through said combustion chamber, and means for receiving combustion products from said chamber and curing them under controlled conditions.
 16. The invention of claim 15 wherein said curing means comprises a hollow curing chamber, a plurality of conveyors vertically arranged therein and receiving means at the base of the conveyors, said combustion chamber being arranged generally at the top of the curing chamber and further comprising means for directing combustion products from said chamber onto said conveyors.
 17. The invention of claim 16 wherein the plurality of conveyors are operable at different speeds for establishing different curing conditions.
 18. The invention of claim 16 wherein the tops of the conveyors are closely adjacent the combustion chamber to permit preheating thereof. 